Thermal drive method for recovery of oil



1952 E. s. MERRIAM ETAL 2,584,606

THERMAL DRIVE METHOD FOR RECOVERY OF OIL Filed July 2, 1948 fie der;

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Patented Feb. 5, 1952 .UNITED STATES PATENT OFFICE THER A naive Mn'rnon roe RECOVERY OF'OIL Edmund S. Merriam, Marietta, Ohimand Frederick squires, Champaign, Ill.

Application July 2, 1948, Serial No. 36,668

8 Claims. 1 (01. 166 21).

The present invention relates to the production of oil, and moreparticularly to an improved method in which heat is generated in the production horizon and is directly-applied to the oil-containing reservoir to provide a ther-- mal drive forrecovery of the'oil.

Petroleum is generally found insandstones or porous limestone situated between impervious layers of shale or the like. Initially, the oil is usually found to be associated with lighter hydrocarbons such as methane and ethane, which may exist as free gases in contact with the oil or dissolved in the oil. When such oil bearin sands are reached by drilling, the expansive force of the gas, either free or-dissolved under the pressure existing at the depthof the oil reservoir, moves oil and gas toward the region of low pressure around the well bottom. With conditions at the casinghead uncontrolled, the rapid flow of oil and gas from the'well creates a gusher and fiush production results. After'the initial pressureexisting has diminished with the escape of most of the gas associated with theoil from the well, the motive power bringing oil to the surface is largely dissipated. At this stage, the well is put to pumping with resultant increased production of oil from the well together with "additional amounts of gas. produced by pumping diminishes to the point where pumping is no longer economical. The remaining oil has little pressure exerted upon it by the small amount of residual gases or vapors remaining in the reservoir and the heavier hydrocarbons present assume a more viscous, semi-solid state which tends to choke the pores of the sand preventing drainage of the oil to the well bottom.

In time the flow of oil In an attempt to increase productivity of such wells, the method of repressuring has been adopted. This operation involves forcing back into selected central wells either natural gas taken from other wells or air. The gas injected into the selected well under pressure. passes through the porous oil-containing sands and is vented from adjacent wells. By this procedure, the gas mechanically forces some of the heavier oil into the well bottoms, and entrains any hydrocarbons existing in vapor forni in the reservoir.

Upon continued operation, this method alsobecomes unprofitable and it must be abandoned even though the reservoir is only partially depleted with respect to the oil initially present.

Further attempt to increaseproduction from such wells involves final resort to the so-calledt flooding procedure. .Inthis procedure water under'pressure is injected into selected wells and the entire oil reservoir is scoured with water bringing to the surface from adjacent venting Wells a further portion of the residual oil. After practicing this method the oil field can no longer be utilized for further production.

It is well-known, that oil fields which have been subjected to the foregoing successive treatments still contain in the sands about half of the oil known to be initially present.

It has been recognized heretofore, that the application of heat to the oil-containing sands tends to increase production of oil from oil reservoirs. For example, it has been proposed to inject heated gaseous products of combustion into partially depleted oil reservoirs in an attempt to drive out the residual oil by reducing the visccsity and thereby facilitating flow. In some instances, combustion of the oil itself has been proposed as the source of heat.

It has also been proposed to utilize steam under pressure by passing the same through the oil-containing sands. Such procedures have serious and inherent disadvantages which are common to all, and, in addition, further disadvantages are' to be found which are specific to each method.

One of the main disadvantages common to above procedures is the loss of heat amounting to a major portion of the total heat input. Upon injection of heated gaseous products of combustion orsteam into an open well, heat will spread in all directions from the bottom of the well by conduction. Since the heat conductivity of the oil-containing sands and the adjacent impervious shale strata are of approximately the same order of magnitude, regions of equal temperature (isotherms) will approximate concentric spheres with the bottom of the well at the center of the sphere. In other words, heat will travel outwardly, horizontally and vertically, the mass of rock being heated varying with the cube of the radius from the well center. In addition, much of the sensible heat contained in the gaseous products of combustion will be vented through the open well. In an attempt to reduce these serious heat losses, the, input well has been closed and pressure developed to drive the hot products of combustion into the porous oil-containing sands to increase the travel of heat horizontally toward the venting or producing wells communicating with the oil sands. Thus, the enlarging surfaces of equal temperature (isotherms) tend to take the form of an oblate spheroid. However, with increasing passage horizontally oi the heat, a greater portion is dissipated, and loss by conduction vertically away from the oil-containing sands increases. Thus, with a steady heat input a very appreciable portion of the total heat is lost by conduction vertically into and through the layers of shale, although the movement of the heat in a horizontal direction through the oil-containing sands is somewhat more extensive.

it is a primary object and purpose of the present invention to provide an improved process for the recovery of oil from oil reservoirs whereby optimum portions of the hitherto unrecoverable oil may be produced.

It is a further object of the invention to provide an improved method. of thermal drive for heat losses.

Still another object of the invention is to pro!- vide a thermal drive method for the production of oil in which both sensible heat and latent heat of the heating mediums are fully utilized and perform interdependent functions.

A further object of the invention is to provide an improved method of recovery of oil in which there is a minimum loss of oil due to uncontrolled oxidation and combustion thereof.

A still further object of the present invention is to provide a method. for the recovery of oil in which the tarry residues of the oil are utilized.

Another object of the present invention is to provide a novel type of gas burner adapted to operate at pressures in excess of existing well pressures.

These and other objects and advantages of the present invention will become apparent from the following detailed description thereof.

The method of the present invention generally comprises introducing a combustible gas and a combustion supporting gas into a selected portion of an oil reservoir, producing combustion of said combustible gas therein, introducing an up heated fluid into the selected portion of the oil reservoir, and recovering the oil from another selected portion of the reservoir.

The method of the invention is preferably practiced by utilizing an existing oil well communicating with the oil reservoir asthe input well, and "employing one or more existing adjacent wells as the venting wells. however, new venting wells may be drilled closer to the selected input wells. The bottom of the input well constitutes a combustion chamber into which a combustible gas and a combustion sup porting gas such as air are introduced under pressure. The combustion supporting gas may be air, oxygen, or mixtures thereof, or any permanent gas containing sufficient oxygen to effect good combustion. The combustible gas may be any heating gas such as producer gas, water gas or natural gas. The input well is capped or closed in at the casinghead so that any desired pressures may be developed. Upon ignition and continued combusion of the gas,

If necessary,

heatedgaseous produetsof combustion are developed, which under the existing pressure are forced into the oil reservoir.

The heat imparted in this manner to the oil in the sands volatilizes a portion of the oil and reduces the viscosity of the remaining heavier constituents of the oil tend ing to fluidize the same. The vaporized portions portions of the oil are mechanically forced un-.

der pressure of the gaseous products of 00.. bustion toward the venting well. As the vaporized portions of the oil move into cooler regions of the oil-containing sands, they are partially condensed and release the latent heat of condensation at that point, which together with the sensible heat in the gaseous products of combustion serves to increase the temperature in regions of the sands more remote from the input well. Thus, the entire oil reservoir is progressively heated and the oil in vaporous and/or fluid state is forced into the venting well bottom where it is removed by ordinary pumping means. vaporization of a portion of the oil, and, in addition, formation of steam from the connate water adds to the total volume of gases, facilitating removal of the oil from the reservoir.

With increasing temperature in the oil reservoir, the additional air in excess of that supplied to the burner causes partial oxidation of some of the heavier components of the oil. This oxidation forms pitch-like bodies in the oil. These burn at the higher temperatures developed later producing additional heat liberated in situ in the oil-containing sands, which i'urth r aids in driving the oil from the sands toward the venting well.

One of the principal features of the present invention is the reduction of heat losses due to conduction of heat vertically from the well bot tom where combustion occurs. This reduction of heat losses is accomplished through reversal of the flow of heat away from the combustion chamber in a vertical direction by reversing temporarily the temperature gradient existing from the combustion chamber through the adjacent shale strata. The invention further provides for redirecting in a horizontal direction through the oil-containing sands of the oil reservoir, the heat regained by reversal of the flow. This elimination of heat losses according to the method of the present invention may efiected in any one of several ways and either by means of a cyclic process or a continuous process.

According to one embodiment of the invention, combustion at the bottom of the input well is maintained for a suitable period of time until the gaseous products of combustion have sufliciently penetrated the oil-containing sands. During this time an appreciable amount of the totalheat input moves away from the combustion chamber and the input well bottom by conduction in a vertical direction through the shale strata adjacent to the oil-containing sands of the reservoir. At the end of this period flow of the combustible gas is shut off and combustion ceases. However, the introduction of air under pressure is maintained. Thus, cold air entering the bottom of the hot well abstracts heat from the walls of the well thereby becoming heated. The heated air under the existing pressure is forced horizontally through the oil sands. A continued supply of 'cool air into the well bottom progressively lowers the temperature of the well to a point where the well becomes cooler than the surrounding rock or shale. At this point the temperature gradient previously existing from the well toward the shale strata is reversed, and a flow of heat is initiated from the shale strata back toward the well. The heat thus regained into the well bottom serves to further heat the air which passes horizontally into the oil-containing sands. Thus, an appreciable portion of the heat lost byv vertical conduction is regained.

Under. continuous heat input, such heat would bepermanently lost. Aiter asuitable interval or recuperating some of this .lost heat, combustion is again initiated, and the cycle is repeated. The time in which a complete cycleoccurs may be widely varied depending on conditions existing in the oil field. For example, onecyclexmay be from a few hours to several days. Thecoolair phase of the cycle should not be prolonged to the extent that undue cooling of the oil. sands occurs. The advantageous result is an increase'of the flow of the total heat input horizontally into the oil-containing sands of the reservoir, and a sub' stantial reduction in the heat losses due to conduction vertically into the adjacent rock or-shale;

A preferred alternative procedure for reducing heat loss and increasing both the thermal, and mechanical eflicieney of the process is set forth in the following embodiment of the invention. Combustion is initiated at the well bottom and maintained for a period suflicient to insure penetration of the heated gaseous products of combustion into the oil-containing sands. .At this time combustion is stopped by shutting off either the air or gas supplied to the burner and a stream of water is introduced into the input well. Upon contacting the very hot well bottom, the water flashes into steam developing a high pressure under which it is forced into the oil-containing sands of the reservoir. The steam created penetrates the oil sands, previously heated by the gaseous products of combustion, until it has tra versed the entire portion of oil sands existing at a temperature above the condensation point of the steam at the existing pressure of the reservoir. Thus, the steam passes on into the sand to a cooler region where it condenses, releasing latent heat of condensation and rapidly warming the adja-, cent oil sands.

When the water flashes to steam in the not well bottom all of the necessary latent heat of vaporization is absorbed by the Water from its surroundings, and thus heat is abstracted from the walls of the well. As water is continuously introduced into the well bottom, it continuously abstracts heat from the surroundings. The temperature gradient existing from the well bottom through the adjacent rock or shale will be reversed when the temperature of the well becomes lower that that of the surrounding shale strata. It is an important advantage of this embodiment of the invention that the well bottom is much more rapas a cooling medium. The flash evaporation of the water at the well bottom with the attendant water at the Well bottom with the attendant absorption thereby of the latent heat of vaporization rapidly cools the Well bottom to a point at which the temperature gradient reverses. The reversal of the temperature gradient in'turn causes heat to flow from the surrounding rock or shale back into the well bottom where the heat is imparted to the steam which penetrates the oi1- containing sands and thus redirects the flow of regained heat in the desired horizontal direction. Combustion is again initiated at the well bottom when the temperature reaches a predetermined point, and the cycle is repeated. The time period of the cycle may be widely varied. Preferably one cycle is completed in about one day.

The foregoing embodiments of the invention are conducted in a cyclic or alternate manner. The method may also advantageously be conducted in a continuous manner according to another alternative embodiment. Combustion of the gas in the input well bottom is continuously maintained and a continuous stream of water is introduced into the well bottom. Thus,

the heat developed by the continuous -combus tion existing primarily as sensible heat in the gaseous products of combustion effects a continuous vaporization of the water into .supers heated steam at the well bottom. A high pressure is developed in the well bottom resulting from generation of the gaseous products of combustion and steam. Under this existing pressure both the gaseous products of combustion and the superheated steam forcibly penetrate the oil-containing sands of the reservoir. Heat loss by vertical conduction of the sensible heat in the gaseous products of combustion from the input well bottom into the adjacent strata of rock or shale is substantially eliminated, since an appreciable portion of this heat .is absorbed by the contin uously supplied water as latent heat of vaporization and the steam created moves horizontally into the oil sands. This heat extracted from the products of combustion by the water in the well bottom efiectively maintains a lower temperature in the well bottom and is carried horizontally into the oil-containing sands where it is released as latent heat of condensation when the steam comes into contact with regions of the sands which are at a lower temperature than the temperature of the condensation of the steam at the existing pressure in the oil reservoir.

The present invention also provides a gas burner of the surface combustion type adapted for operation at the pressures existing in the input well bottom. The burner is also adapted to operate in the presence of Water and water vapor.

The method and apparatus of the present invention are more fully described in detail With reference to the accompanying drawings which are illustrative of preferred embodiments thereof, and are not intended to constitute a limitation oi the invention, in which:

Figure 1 is a diagrammatic view partly in section of an oil field showing the apparatus by which the method. of invention is practiced;

Fig. 2 is an enlarged View, partly in section showingthe novel gas burner positioned in the input well bottom; and

Fig. 3 is an enlarged sectional view take on line 3-3 of Fig. 2 showing further details of construotion of the burner.

Referring now to Fig. 1, A represents an oil reservoir containing residual oil and porous sandstone or limestone. Communication from the surface to the reservoir is established through input well I and venting we1l2. The gas burner 3 of the present invention is lowered into the bottom of the input well and the casinghead is then capped. Air and the gas under pressure in excess of that existing in theoil reservoir are introduced through lines 4 and .5 to the duct 5' connected to the burner 3 at the well bottom. Additional air under pressure is injected from line i into the casing of the Well. The combustible mixture of air and gas issuing from the burner at the well bottom may be ignited by any.

or air lock. The heated gaseous products of combustion resulting from operation of the gas burner are forced through the oil-containing sands of the reservoir under the pressure developed with the input well closed. The isotherms B shown in Fig. 1- represent the flow of heat from the well bottom due to conduction and passage of the gaseous products of combustion into the oil sands. It will be seen that the isotherms are approximately of the form shown and that appreciable amounts of heat developed in the well bottom are dissipated by heating the adjacent strata of rock or shale.

After combustion has ensued for a time sufficient to insure heating of the oil sands by passage of the gaseous products of combustion therethrough, valves 8 and in lines 4 and are closed while valve H in the excess air line 1 remains open. This effectively shuts down operation of the burner in the input well bottom and permits continued flow of cool air under pressure through line i to the input well bottom. The continuous supply of air progressively cools the well bottom until the temperature gradient existing between the well bottom and the adjacent strata and rock or shale is reversed so that heat dissipated by conduction into the rock flows back into the well heating the incoming air. The air thus heated continues in its path of movement under pressure in a horizontal direction into the oil-containing sands of the reservoir.

The products of combustion together with excess air progressively penetrate through the sand and reach the venting well. The oil sands, of course, are hottest at the input end, but are gradually, continually and progressively heated until the heat reaches the venting well with the products of combustion and excess air. The portions of oil thermally driven into the venting well which are in the vapor state are removed to a suitable stripping plant for extraction from the gaseous products of combustion and the excess air. A pump i2 is provided for the venting well 2 to remove liquid hydrocarbons of the oil driven out of the sands into the well bottom.

In the cyclic procedure of the invention embodying the use of steam, after a suitable period of time during which the burner is in operation, valves 8 and it are closed, completely shutting off the flow of air and gas to the input well bottom. Thus, the flame issuing from the gas burner 3 is extinguished. A slow stream of water is then introduced into the well bottom from line 9 through piping l3 by opening valve l4. Upon contact with the highly heated well bottom, the water flashes into steam and is forced into the oil-containing sands of the reservoir. The steam continues its passage through the oil-containing sands until it reaches a region below its condensation temperature at the existing pressure in the reservoir. At this location the steam condenses releasing all of its latent heat of vaporization thereby warming the oil in the formation in that vicinity. By continued condensation of steam, the latent heat of condensation released sufficiently warms the oilcontaining sands at the situs where condensation has taken place so that continued condensation of the steam does not occur at the same location. The warming which occurs allows the steam to move farther into the sands toward the venting well before condensation again occurs. Thus, the sands are progressively heated until the steam reaches the venting well.

The continuous vaporization of the water into steam by flashing during this phase of the method, rapidly cools the walls of the input well and of the method. At this point the temperature gradient reverses and heat flows from the heated shale or rock into the well bottom generating additional steam which continues to pass in a horizontal direction into the oil sands. Thus, the heat dissipated into the strata of shale or rock is regained and redirected into the oil sands in the form of latent heat contained in the steam. The cycle is then repeated until the well is no longer productive of oil.

In the alternative procedure embodying continuous operation, valves 8 and It are initially open whereby the mixture of combustible gas and air flows through lines 4 and 5 to duct 6 and into the gas burner 3 at the input well bottom. Valve '1 is open to supply excess air under pressure through line 1 and the burner is ignited. Valve I4 in waterline 9 is then opened permitting flow of a slow continuous stream of water through piping I3 into'the input well bottom. Thus, the sensible heat contained in products of combustion from the continuously operated burner 3 is in part utilized in supplying the latent heat of vaporization which effects continuous vaporization of the water introduced into the input well bottom. The resulting mixture of heated gaseous products of combustion and steam are forced by the pressure developed in the input well bottom through the oil-containing sands where they heat and vaporize and iiuidize the residual oil. The oil is driven mechanically or by entrainment in the gases into the venting well and. is removed therefrom through line 15 with the aid of pump l2. Line l6 conducts gas and vapor to a processing plant.

The sensible heat of the gaseous products of combustion produced by operation of burner 3 is not dissipated by vertical conduction into the surrounding strata of rock and shale, but is primarily utilized to vaporize the water continuously supplied to the Well, which in the form of steam is then horizontally forced through the oil-containing sands. Thus, most of the total heat input into the system is utilized for the desired purpose of heating the oil-containingsands.

In this method of operation the well bottom and adjacent portions of rock serve as the equivalent of a steam boiler. Although the burner itself may be at a high temperature the continuous supply of water prevents the rock and well bottom from attaining temperatures much in excess of the temperature of water boiling under the prevailing pressure. The relatively low temperatures do not favor loss of heat in a vertical direction. Such losses would be favored if the rock were heated to a much higher temperature, as would be the case if products of combustion alone carried the heat. 7

Use of liquid water in conjunction with a burner favors the horizontal movement of heat and minimizes the undesirable losses in a vertical direction.

Referring now to Figure 2, the construction and operation of the novel gas burner 3 is described in detail. In this figure, the gas burner 3 is inserted into the well 1 inside of casing 20 so that it is positioned centrally within the shot hole 2| at the well bottom. The burner 3 pcsitioned in the shot hole 21 is attached to tubing consisting of a central pipe 22 for supplying gas located within an outer pipe 23 inserted through the casinghead of the well for supplying air. The outer annular duct formed by pipes 22 and 23. .and the. cylindricalduct within pipe 22 are assaeoe stem valve 24 positioned in tapered end 25 of .pipe 22 and an annular duct 26 formed by baffle 27 positioned within the pipe 23. An elongated stem 28' is connected to valve 23 and extends through pipe 22 at the top of the tubing where a wheel or handle 29 is attached. This provides a means of finely adjusting the ratio of air and gas fed to burner 3.

A mixing chamber 3! is connected to battle 2'! and comprises a cylindrical body having mu1- tiple constrictions 3| therein.

A lower extension 32 of pipe 23 carries a metal cage 33 comprising a metalbase portion 32 and spaced vertical rods 35 extending upwardly therefrom. The rods 35'are attached at their upper ends to a threaded metal ring 35. A hollow cylinder of porous ceramic material 3'! is inserted into the lower annular extension 32 of pipe- 23, which is threaded on its external periphery. Thus cylinder 31 is fixed in position on extension 32 by means of the threaded metal ring 3Eand the base 3 3 of cage 33. The ceramic cylinder 3'5 may be made of suitable heat insulatin or refractory material such as brick, or the like, used for furnace linings. The porous cylinder 31 contains a cavity 38 tapering toward the inlet end which communicates with the chamber 30. This cavity 33 which constitutes the combustion chamber of burner 3 is filled with granular refractory material. Cylinder 3'! is provided with a number of horizontal ports 33 which are so located that they lie in different vertical planes than the rods 35 of the cage 33. (This structure is more clearly shown in Fig. 3.)

A combustible gas under regulated pressure is fed into pipe 22 through line in which is inserted appropriate regulators and flow meters. Air under regulated pressure is supplied to the pipe 23 surrounding the pipe 22 through line 4 passing through an appropriate regulator, flow meter and valve 8. Thus, the ratio of air to gas may be maintained constant or may be varied. For example, the ratio of gas to air may be one cubic foot of gas to ten cubic feet of air. The air and gas introduced into pipes 22 and 23 mix in the mixing chamber 30 upon passage through duct 26 and valve 24', respectively. A main air supply is introduced into casing 2i through line 1 controlled by valve ii. The pressure of the main air supply is maintained at a value lower than the pressure of the air and gas fed to the burner. The combustible mixture of gas and air issuing from the ports 39 in the ceramic cylinder 31 of the burner 3 may be ignited by any suitable means such as described above. When thus ignited, the flame pops back into the cavity 38 of the ceramic cylinder 3?. A static zone of burning is established within the cavity 38 when the velocity of the explosive back flash equals the forward flow of the gas and air mixtures through chamber 30 into cavity 38. At this point combustion becomes even and continuous. As long as the pressure existing outside of the porous cylinder 31 of the burner is not permitted to exceed the pressure of the forward flow of combustible gas and air fed to the burner, the burner will operate continuously. The temperature of the products of combustion and the excess air from the main air supply will depend upon the ratio of combustible gas and air fed to burner 3, and also on the ratio of air supplied through the main air supply. The

refractory material inside of the burner'3 may reach a temperature of 3500 EL, where it is in direct contact with'the flame. However, the metal parts of the cage 33 of the burner will not be subject to excessive temperatures.

Figure 3' merely advantageously illustrates the construction of the burner 3 relative to the ports 39 in porous cylinder 3? and metal cage rods 35. From this figure it is clearly seen that the vertical rods 35 are disposed in vertical planes which i are not common to the vertical planes occupied by ports 32 in'cylinder 3?. hi this construction,

direct impingement of the flame or hot gases of combustion upon rods 35 is avoided.

The burner also operates efliciently under the conditions present in the alternative procedures "of theinvention involving supplying a continuous supply of water to the well bottom. As long as the pressure of the wa er outside of the porous ceramic cylinder 3? of the burner 3 does not exceed the pressure of the forward flow of gas and air fed to the burner, the burner will continuously operate.

The method of the present invention is more efiieient than those heretofore practiced, since heat losses are largely reduced.

Furthermore, the preferred embodiments of the invention involving the use of water supplied to the input well, combined with operation of the gas burner, either in a cyclic manner or continuous manner, presents many advantages over the use of either steam alone or products of combustion alone. Not only are heat losses eliminated or reduced to a minimum by the flash vaporization of the water introduced into the input well, but the latent heat of condensation of the steam is realized in heating the oil in the oil-containing sands while avoiding the disadvantages encountered when using steam alone.

The process described produces the more volatile and more valuable parts of the oil, and burns the non-volatile valueless parts, thus furnishing part of the necessary heat.

Having thus described our invention, we claim:

1. A cyclic method for the recovery of oil from an oil-bearing geological formation which comprises alternately practiced steps (a) and (b), said step (a) comprising introducing into said formation through an input well, at a pressure greater than that extant therein, a combustible gaseous mixture, effecting combustion of said mixture in said formation to produce hot products which penetrate said. formation and impart heat to and reduce the viscosity of the oil present therein, said combustion products and said oil being moved through said formation toward a venting well; said step (12) comprising introducing a stream of fluid heat transfer medium through said input well into that portion of said formation where combustion was effected in step (a) to heat said heat transfer medium, causing the so-heated transfer medium to penetrate said formation to impart heat to and reduce the viscosity of the oil present therein, said heat transfer medium and said heated oil being moved through said formation toward aventing well, said steps (a) and (2)) being alternated at ap propriate intervals.

2. The process of claim 1 in which the fluid heat transfer medium is air.

3. The process of claim 1 in which the fluid heat transfer medium is water which is converted to steam upon introduction into the formation through the input well, and in which step (b) is discontinued and step (a) is repeated when the heat requisite to effect such conversion of water into steam has been dissipated.

4. A method for the recovery of oil from an oil bearing geological formation having an input well and a venting well, which comprises introducing through said input well, into said formation, a combustible, gaseous, mixture, at a pres sure in excess of that existing in said formation, and water, effecting combustion of said mixture in said well to produce combustion products and steam, under a pressure sufficient to cause said combustion products and steam to penetrate into said formation toward a venting well to impart heat to and reduce the viscosity of the oil present in the formation, and recovering oil from a venting well.

5. The process of claim 4 wherein the combustible, gaseous, mixture employed is producer gas.

6. The process of claim 4 wherein the combustible, gaseous, mixture employed is water gas.

7. 'The process of claim 4 wherein the combustible, gaseous, mixture employed is natural gas.

8. A method for the recovery of oil from an oil bearing geological formation having an input well and a venting well, which comprises continuously introducing through said input well, into said formation, a combusible, gaseous, mixture, at a pressure in excess of that existing in said formation, and water, efiecting combustion .12 of said mixture in said Well to produce combustion products and steam, under a pressure sufficient to cause said combustion products and steam to penetrate into said formation toward a venting well to impart heat to and reduce the viscosity of the oil present in the formation, and recovering oil from a venting well.

EDMUND S. MERRIAM.

FREDERICK SQUIRES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 797,529 Oliphant et al Aug. 15, 1905 895,612 Baker Aug. 11, 1908 1,449,420 Kreager et a1 Mar. 27, 1923 1,473,348 Howard Nov. 6, 1923 1,913,395 Karrick June 13, 1933 1,961,751 Feyling June 5, 1934 2,188,737 Hixon Jan. 30, 1940 2,241,253 Garrison May 6, 1941 2,258,614 Kendrick Oct. 14, 1941 2,344,400 Ehnbom Mar. 14, 1944 2,390,770 Barton et al. Dec. 11, 1945 2,444,755 Steffen July 6, 1948 2,506,853 Berg et a1. May 9, 1950 

4. A METHOD FOR THE RECOVERY OF OIL FROM AN OIL BEARING GEOLOGICAL FORMATION HAVING AN INPUT WELL AND A VENTING WELL, WHICH COMPRISES INTRODUCING THROUGH SAID INPUT WELL, INTO SAID FORMATION, A COMBUSTIBLE, GASEOUS, MIXTURE, AT A PRESSURE IN EXCESS OF THAT EXISTING IN SAID FORMATION AND WATER, EFFECTING COMBUSTION OF SAID MIXTURE IN SAID WELL TO PRODUCE COMBUSTION PRODUCTS AND STEAM, UNDER A PRESSURE SUFFICIENT TO CAUSE SAID COMBUSTION PRODUCTS AND STEAM TO PENETRATE INTO SAID FORMATION TOWARD A VENTING WELL TO IMPART HEAT TO AND REDUCE THE VISCOSITY OF THE OIL PRESENT IN THE FORMATION, AND RECOVERING OIL FROM A VENTING WELL. 